During the fabrication of III-V optoelectronic devices, it is often beneficial to be able to characterize the physical properties of the various layers forming the device. For example, electro-absorption modulated lasers (EMLs) require a large extinction ratio (e.g., &gt;21.0 dB) in order to provide an acceptable level of performance. The extinction ratio is dependent upon a number of factors, such as the quantum well structure, the width of the active region, and the p-i junction placement. For an optimal extinction ratio, the applied field must be present only across the active region. Further, knowledge of the p-i junction position is critical in preventing over-diffusion of zinc (a p-type dopant in EML devices) into the structure.
In the prior art, correlation of a device parameter such as the extinction ratio with the wafer level material properties has been accomplished by employing Secondary Ion Mass Spectroscopy (SIMS) analysis. With the SIMS analysis, the position and carrier density of the p-type zinc dopant can be monitored with respect to the active region. However, this method is destructive and can only be performed on a sample basis. To date, there has been no method established for monitoring the characteristics of each wafer containing EML devices as they are processed.